The invention relates to a system for performing myocardial revascularization on a beating heart of a patient.
Transmyocardial revascularization (TMR) is a surgical treatment for cardiovascular disease. Present TMR procedure uses a laser beam to drill holes of approximately 1 mm diameter through the myocardium, typically into the left ventricle. These holes or channels extend through the entire heart wall thickness from the outside through to the ventricle. The openings of the channels on the outside surface of the heart heal due to external pressure from the surgeon, but the channels remain open on the inside, allowing blood to enter the heart wall tissue from the ventricle.
In another approach myocardial revascularization can be performed using a catheter introduced percutaneously so that the tip of the catheter is inside a chamber of the heart, typically the left ventricle, where the holes or channels can be created from the inside toward but not through the outside of the heart. This approach is also known as endocardial laser revascularization (ELR), percutaneous myocardial revascularization (PMR), and direct myocardial revascularization (DMR). The channels are drilled with a laser beam introduced through the catheter. The catheter typically is an 8-French or 9-French catheter.
Certain problems are presented when laser revascularization is done on a beating heart. A beating heart presents a moving target, which can make it difficult to accurately and consistently form channels of a desired depth and size. The heart also is extremely sensitive to a laser pulse at certain times during its cycle. A laser pulse striking the heart during the T wave of the heart beat cycle could cause the heart to fibrillate and result in complications. While one could stop the heart during the process of TMR, this poses other risks to the patient and complicates the operating procedure. The heart must be cooled and the patient connected to a heart-lung machine.
However, the risk of inducing a beating heart to fibrillate is greatly reduced when the laser is fired only during the refractory period of the heart cycle between the R and T waves of the EGG signal. An additional benefit of firing the laser only between the R and T waves is that this is the period of the heartbeat cycle during which the heart is most still and channels can be formed most accurately. Rudko U.S. Pat. No. 5,125,926 describes a heart-synchronized pulsed laser that fires a laser only during the refractory period of the heartbeat cycle. The patent describes an open chest procedure using an articulated optical arm or a fiber optic element to deliver the laser beam to a surface of the heart.
Aita U.S. Pat. No. 5,389,096 discloses a percutaneous myocardial revascularization procedure in which a steerable heart catheter is guided from the femoral artery via the abdominal artery into the left ventricle. The laser energy is delivered through the working channel of the catheter by a fiber optic delivery system.
In one aspect, the invention features, in general, a myocardial revascularization system that includes a laser energy source, an outer guide member providing access to a patient""s heart, and an optical fiber. The optical fiber is coupled to receive laser energy pulses from the source, is slidably located within the guide member, and is extendible from the distal end of the guide member. A drive motor is connected to the fiber to automatically move the distal end of the optical fiber with respect to the distal end of the guide member. A controller controls the drive motor to automatically move the fiber in synchronism with firing of the laser energy.
In another aspect, the invention features, in general, a myocardial revascularization system that includes a laser energy source, an outer guide member providing access to a patient""s heart, an optical fiber that is slidably located within the guide member, and a drive motor connected to the fiber to automatically move the distal end of the optical fiber with respect to the distal end of the guide member. A controller controls the drive motor and automatically calibrates the position of the distal end of the fiber with respect to the distal end of the catheter.
In another aspect, the invention features, in general, a myocardial revascularization system that includes a semiconductor laser energy source (e.g., a diode laser) that outputs laser pulses having a wavelength between 600 nm and 1000 nm, an optical fiber that is coupled to receive laser energy pulses from the source and to deliver them to a patient""s heart tissue to be revascularized, and an outer guide member that engages the fiber and permits an operator to direct the tip to contact the patient""s heart tissue to be revascularized.
In another aspect, the invention features, in general, a myocardial revascularization system that includes a laser energy source, an optical fiber that is coupled to receive laser energy pulses from the source and to deliver them to a patient""s heart tissue to be revascularized, and an outer guide member that engages the fiber and permits an operator to direct the tip to contact the patient""s heart tissue to be revascularized. The fiber has, at its tip, a heat absorbing material that is nonmetallic and is partially transparent to the pulses.
In another aspect, the invention features, in general, a myocardial revascularization system that includes a laser energy source, an optical fiber that is coupled to receive laser energy pulses from the source and to deliver them to a patient""s heart tissue to be revascularized, and an outer guide member that engages the fiber and permits an operator to direct the tip to contact the patient""s heart tissue to be revascularized. The fiber has an enlargened portion at the tip thereof that has a transverse dimension that is larger than the fiber diameter.
In another aspect, the invention features, in general, a myocardial revascularization system that includes a laser energy source, an outer guide member providing access to a patient""s heart, and an optical fiber that is coupled to receive laser energy pulses from the source and is slidably located within the outer guide member. The outer guide member is 7 French or smaller and has a deflectable distal end that is deflectable by an operator-controlled mechanism.
In another aspect, the invention features, in general, a myocardial revascularization system that includes a laser energy source, an outer guide member providing access to a patient""s heart, and an optical fiber that is coupled to receive laser energy pulses from the source and is slidably located within the outer guide member. A lubricant is located between the optical fiber and an inner lumen surface of the guide member.
In another aspect, the invention features, in general, a myocardial revascularization system that includes a laser energy source, an outer guide member providing access to a patient""s heart, and an optical fiber that is coupled to receive laser energy pulses from the source and is slidably located within the outer guide member. A first position sensing component is carried by the optical fiber at or near the distal end of the fiber, and a second position sensing component is carried by the guide member at or near the distal end of the guide member.
In another aspect, the invention features, in general, a myocardial revascularization system that includes a laser energy source, an outer guide member providing access to a patient""s heart, and an optical fiber that is coupled to receive laser energy pulses from the source and is slidably located within the outer guide member. The guide member has a distal end having a non-slip structure for engaging a surface location of a patient""s heart tissue.
In another aspect, the invention features, in general, a percutaneous myocardial revascularization system that includes a laser energy source, a catheter for percutaneous access to a patient""s heart, an optical fiber that is coupled to receive laser energy pulses from the source and is slidably located within the catheter. An inflation balloon is carried on the catheter at the distal end so as to prevent piercing the heart tissue of the patient with the catheter.
In another aspect, the invention features, in general, a percutaneous myocardial revascularization system that includes a laser energy source, a catheter for percutaneous access to a patient""s heart, an optical fiber that is coupled to receive laser energy pulses from the source and is slidably located within the catheter, and a lubricant on the outer surface of the catheter.
Particular embodiments of the invention may include one or more of the following features. The fiber can be automatically advanced by the drive motor. The controller can receive signals indicating the patient""s heart beat cycle (e.g., ECG signals) and synchronize laser firing and fiber movement to the patient""s heart beat cycle. The fiber can be advanced after a short delay after initiation of firing of the laser. The laser firing can be synchronized to occur after the R wave of an ECG signal and to end at a time before the T wave. Alternatively, the laser firing can be synchronized to begin after the T wave and to end at a time before the next T wave.
In particular embodiments, the distal end of the outer guide member can be deflectable to varying amounts of tip deflection (e.g., up to 90 degrees or 120 degrees); a sensor can sense the extent of deflection and generate a signal indicating the extent of deflection, and the controller can receive the signal indicating the extent of deflection and determine a calibration adjustment for the position of the distal end of the fiber with respect to the distal end of the guide member as a function of the guide member deflection.
In particular embodiments, the controller can use the calibration adjustment to cause the fiber tip to be moved to an initialized position (e.g., about 1 mm) prior to firing the laser. The controller can fire the laser after moving the fiber to the initialized position, and after receiving a fire signal from the operator. The controller can fire the laser after receiving an ECG signal after receiving the fire signal. The controller can advance the fiber after a delay of about 50 ms after initiating firing of the laser. The controller can advance the fiber a predetermined distance (e.g., at least 4 mm or at least 10 mm) in a predetermined period (e.g., less than 300 ms, though it can be greater than 300 ms) while continuing to fire the laser. The predetermined period can start after the R wave and end before the T wave. Alternatively, the predetermined period can start after the T wave and end before the next T wave. The predetermined period can be contained within one heart beat cycle or within more than one heart beat cycle. The predetermined period can include a period before the T wave and a period after the T wave wherein the laser is not fired and the fiber is not advanced during the T wave.
In particular embodiments, the controller can retract the fiber after discontinuing firing of the laser. The controller can cause the laser to fire a burst of energy as the fiber is being removed from the channel to coagulate the entrance to the channel in (TMR applications).
In particular embodiments, the drive motor used to move the fiber can be a stepper motor. The stepper motor can cause a fiber engagement member that engages a portion of the fiber external of the patient to be moved with respect to the outer guide member. The fiber engagement member can be moved by the stepper motor with respect to a handle to which the outer guide member is attached. A sheathed cable can be connected between the stepper motor and the handle. The sheathed cable can include an outer sheath that is secured to the fiber engagement member and an internal cable that is connected to the handle, such that, retraction of the internal cable within the outer sheath by the stepper motor causes the fiber engagement member to be moved toward the handle and the fiber to advance within the outer guide member.
In particular embodiments, the system can include a drug delivery system that delivers drugs from the distal end of the catheter in response to a drug delivery signal, and the controller can control the drive mechanism to move the fiber in synchronism with delivery of the drugs from the distal end of the catheter. Drug delivery can be synchronized to occur during movement of the distal end of the fiber away from the patient""s heart tissue. The drug delivery can be synchronized to occur as the distal end of the fiber is removed from a channel formed in the heart tissue.
In particular embodiments, energy absorbing material can be located in a coating at an end surface portion of the fiber tip and not at a lateral surface portion of the tip. The energy absorbing material can include a coating of energy absorbing glass. The energy absorbing glass can be a coating of an optical glass filter that absorbs radiation at the wavelength of the laser energy source. The coating can include ionically colored glass. The coating can be about 20-30 um thick. The energy absorbing material can include carbon. The energy absorbing material can include metallic particles in nonmetallic material, e.g., glass. The fiber can be made of silica glass material. The coating can absorb between 5 and 40% (preferably between 15 and 25%) of the radiation directed to it.
In particular embodiments, the fiber tip can have an enlargened portion that has a transverse dimension of greater than about 600 um (e.g., about 700 um), and the fiber diameter can be less than about 500 um (e.g., about 400 um). The enlargened portion can be generally spherical. The enlargened portion can be made by heating the fiber, and the fiber can be made of material selected to have a surface tension so as to provide a 700 um tip dimension in a transverse direction. A lifeline can be attached to the enlargened portion to retain the enlargened portion in the event that it becomes separated from the fiber. The tip can include a material having a different refractive index than the material of the fiber, and a sensor can be used to monitor reflection returned from the interface of the material of the fiber and the material having a different refractive index to thereby confirm that the enlargened portion remains connected to the fiber.
In a particular percutaneous embodiment, the catheter can be 6 French or smaller. The catheter can have a fluoropolymer heat shrink tube over the optical fiber. The optical fiber can have a core diameter less than 800 um (preferably less than 500 um, e.g., about 400 um).
In embodiments employing a lubricant, the lubricant can be provided by a coating that creates a water film when exposed to an aqueous solution. The coating can be a water or solvent based hydrogel.
In embodiments employing position sensing components on the end of the fiber and outer guide member, the first position sensing component can be a magnetic material, and the second position sensing component can be a magnetic position sensor, e.g., a Hall effect sensor. Alternatively, the first and second position sensing components can be radiopaque markers.
Other advantages and features of the invention will be apparent from the following description of particular embodiments and from the claims.